b 1. Field of the Invention
The present invention relates to a method for production of needle coke from filtered liquidified coal tar pitch.
2. Brief Description of the Background of the Invention Including Prior Art
Needle cokes have good graphitizing properties and therefor provide a good starting material for the production of high value graphite electrodes.
It is known to produce needle cokes of good quality from coal tar pitches by liquifying the pitches through heating to a temperature of from 135.degree. to 280.degree. C., removing ash, soot and quinoline insoluble parts by filtration and subjecting the pitches purified in this manner to a coking process. The filtration of the pitches in the absence of a solvent is difficult and very time consuming. Therefor, the process has been employed up to now only on a very small scale in praxis, even though the filtrates from the undissolved pitches result in the best needle coke qualities.
The person skilled in the art knows that upon filtration through sieves of a pore width of from 100 to 220 .mu.m at the beginning of filtration not inconsiderable amounts of unpurified coal tar pitch pass into the filtrate since the average size of the solid particles in the pitches lies in the range of 30 to 60 .mu.m. Thus in reissued U.S. Pat. No. Re. 25,467 the upper limit of the aperture width of the sieves is given as 162 .mu.m.